Subdivision Surface with a hard edge
I can't seem to open your file, but from the pictures you've provided, I tried to recreate the problem and possibly solve it here:

https://youtu.be/S1x6OycmPD0

In the video you can see me going inside the mesh to check if there are any faces on the inside. Make sure to remove them if you see any on yours. Then I select all and clicked "Remove Doubles".

Let me know if the problem persists